The present invention relates to an apparatus and a method for checking loudspeakers of a playback apparatus.
A loudspeaker array is favorably used as a loudspeaker system in a home theater or an AV system. FIG. 13 shows an example of a loudspeaker array 10, which includes many loudspeakers SP1 to SPm arranged (loudspeaker unit). In this loudspeaker array 10, m=256 and the diameter of each loudspeaker is several centimeters, for example. Therefore, the loudspeakers SP1 to SPm are actually two-dimensionally arranged on a plane surface. However, the following description is given under the assumption that the loudspeakers SP1 to SPm are aligned in the horizontal direction for convenience.
Audio signals are supplied from a signal source SS to delay circuits DL1 to DLm, where the audio signals are delayed by predetermined times τ1 to τm, respectively, and the delayed audio signals are supplied to the loudspeakers SP1 to SPm through power amplifiers PA1 to PAm. The delay times τ1 to τm used in the delay circuits DL1 to DLm are described below.
Then, sound waves output from the loudspeakers SP1 to SPm are synthesized and a sound pressure as a synthesis result is obtained at any point. As shown in FIG. 13, in a sound field generated by the loudspeakers SP1 to SPm, predetermined points Ptg and Pnc are defined as follows:
Ptg: a point where the sound pressure is higher than that of any other points, that is, a point of enhanced sound pressure; and
Pnc: a point where the sound pressure is lower than that of any other points, that is, a point of reduced sound pressure.
In this case, a method illustrated in FIG. 14 or 15 can be mainly used as a method for making an arbitrary point the point of enhanced sound pressure Ptg.
That is, in the method illustrated in FIG. 14, assume that                L1 to Lm: respective distances from the loudspeakers SP1 to SPm to the point of enhanced sound pressure Ptg; and that        s: sound velocity.        
The delay times τ1 to τm of the delay circuits DL1 to DLm are set as follows:τ1=(Lm−L1)/s; τ2=(Lm−L2)/s; τ3=(Lm−L3)/s; . . . andτm=(Lm−Lm)/s=0.
In this method, when the audio signals output from the signal source SS are converted to sound waves by the loudspeakers SP1 to SPm and are output therefrom, those sound waves are output while being delayed by the times τ1 to τm, respectively. Thus, all of those sound waves reach the point of enhanced sound pressure Ptg at the same time, so that the sound pressure at the point Ptg is higher than that of any other points.
In other words, in the method illustrated in FIG. 14, time differences occur among the sound waves due to variations in the paths from the loudspeakers SP1 to SPm to the point of enhanced sound pressure Ptg. However, the delay circuits DL1 to DLm compensate for the time differences so that the sound waves focus on the point of enhanced sound pressure Ptg.
In the method illustrated in FIG. 15, the delay times τ1 to τm of the delay circuits DL1 to DLm are set so that the phase wavefronts of progressive waves (sound waves) output from the loudspeakers SP1 to SPm match with each other. Accordingly, directivity is given to the sound waves and the sound waves are directed to the point of enhanced sound pressure Ptg. This system corresponds to the focus-type system shown in FIG. 14 in which the distances L1 to Lm are changed to infinite.
The following Patent Documents are cited as known arts: Patent Document 1 (Japanese Unexamined Patent Application Publication No. 9-233591) and Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2004-172661).